1. Field of the Invention
The present invention relates to a magnetic recording medium, and particularly to a magnetic recording medium having a magnetic layer of a continuous thin film type formed by a so-called oblique vapor deposition.
2. Description of the Prior Art
In order to attain compact winding of video and audio recording tapes, there have been active researches to develop a magnetic recording medium having a magnetic layer of a continuous thin film type.
As a magnetic layer for such a continuous thin film type medium, a vapor deposited magnetic layer composed of e.g. Co, Co-Ni, Co-O or Co-Ni-O is most suitable from a view point of the desired characteristics, which is formed by a so-called oblique vapor deposition method in which the vapor deposition is conducted at a predetermined inclined angle relative to the normal line of the substrate.
The thin magnetic layer formed by such a oblique vapor deposition method is composed of columnar crystal particles which are inclined relative to the normal line of the principal plane of the substrate and which have a length corresponding to the thickness of the magnetic layer. Co, Ni, etc. are present in the columnar crystal particles, and optionally incorporated O is present in the form of an oxide on the surface of the columnar crystal particles.
However, such a magnetic layer has drawbacks such that it is susceptible to oxidation and its corrosion resistance is poor.
Under the circumstances, there have been proposed various protective layers to be laminated on such a magnetic layer to improve its corrosion resistance.
However, if a protective layer is provided, the electromagnetic conversion characteristics will be impaired, and the output and the S/N ratio will be lowered as a result of an increase of a spacing loss attributable to the protective layer.